Combining Defects in a Single Nanographene: A Fully Helical Saddle Ribbon

The controlled preparation of well-defined distorted nanographenes by a bottom-up approach based on organic synthesis permits the direct establishment of unprecedented structure–property relationships in carbon nanostructures. The simultaneous incorporation of various defects in nanographenes affords highly curved structures with novel or enhanced photophysical properties. In this sense, we recently reported a fully helical and saddle-shaped nanographene ribbon containing the first undecabenzo[7]helicene unit. Both its linear and nonlinear optical properties are enhanced in comparison with those of other partially π-extended [7]helicenes. Moreover, the new superhelicene exhibits the highest emission dissymmetry factor (glum) reported to date for a homochiral nanographene. The combination of both nonlinear and chiroptical properties in nanographenes opens up new possible future applications for those distorted nanostructures.This work was supported by the European Research Council (ERC) under the European Union´s Horizon 2020 research and innovation program (ERC-2015-STG-677023) and the Ministerio de Economía y Competitividad (Spain) (CTQ2015-70283-P, BES-2016-076371, IJCI2016-27793 and RyC-2013-12943). E.M. thanks the Fundação para a Ciência e a Tecnologia for financial support (UID/NAN/50024/2013 and IF/00759/2013) (

Undecabenzo[7]superhelicene: a helical nanographene ribbon as CPL emitter

We report the synthesis and characterization of an enantiopure superhelicene nanographene constituted by two saddleshaped and one planar hexabenzocoronene (HBC) units arranged in a helicoidal shape. This is, to the best of our knowledge, the first undecabenzo[7]carbohelicene, i.e., the first fully π-extended [7]helicene. Racemic resolution allowed its chiroptical properties analysis revealing dissymmetry factors in the range of 2×10-3 both in the absorption and in the emission measurements. Remarkably, nonlinear photophysical analysis showed two-photon absorption crosssection of 870 GM at 800 nm and a perfect overlapping between linear, non-linear and chiral emission.-European Research Council (ERC-2015-STG-677023) -Ministerio de Economía y Competitividad (MINECO, Spain): CTQ2015-70283-P -Fundacao para a Ciencia e a tecnologia, Portugal: UID/NAN/50024/2013, IF/00759/2013 -Universidad de Granad

A triskelion-shaped saddle-helix hybrid nanographene

A unique rippled nanographene constituted by 52 fused rings is presented in which six out-of-plane motifs are fully fused into a triangular aromatic surface of ca. 2.5 nm size. Three units of an unprecedented fully lateral π-extended octabenzo[5]helicene together with three units of saddle-shaped heptagonal rings are combined in a single structure leading to a well-soluble warped nanographene. The two pairs of possible enantiomers have been isolated and their linear, non-linear and chiroptical properties evaluated, revealing an outstanding quantum yield and brightness values at low energy together with good chiroptical responses both in the absorption and emissionWe acknowledge the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-2015-STG-677023) and the Ministerio de Economía y Competitividad (MINECO, Spain) (CTQ2015-70283- P, UNGR15-CE-3478, BES-2016-076371 and RyC-2013-12943). E.M. thanks the Fundação para a Ciência e a tecnologia (PTDC/NAN-MAT729317/2017 and PTDC/QUI-QFI/29319/2017). We thank the CSIRC-Alhambra from the University of Granada

Impact of Molecular Organization on Exciton Diffusion in Photosensitive Single-Crystal Halogenated Perylenediimides Charge Transfer Interfaces

The efficiency of organic photodetectors and optoelectronic devices is strongly limited by exciton diffusion, in particular for acceptor materials. Although mechanisms for exciton diffusion are well established, their correlation to molecular organization in real systems has received far less attention. In this report, organic single-crystals interfaces were probed with wavelength-dependent photocurrent spectroscopy and their crystal structure resolved using X-ray diffraction. All systems present a dynamic photoresponse, faster than 500 ms, up to 650 nm. A relationship between molecular organization and favorable exciton diffusion in substituted butyl-perylenediimides (PDIB) is established. This is demonstrated by a set of PDIBs with different intra- and interstack distances and short contacts and their impact on photoresponse. Given the short packing distances between PDIs cores along the same stacking direction (3.4-3.7 angstrom), and across parallel stacks (2.5 angstrom), singlet exciton in these PDIBs can follow both Forster and Dexter exciton diffusion, with the Dexter-type mechanism assuming special relevance for interstack exciton diffusion. Yet, the response is maximized in substituted PDIBs, where a 2D percolation network is formed through strong interstack contacts, allowing for PDIBs primary excitons to reach with great efficiency the splitting interface with crystalline rubrene. The importance of short contacts and molecular distances, which is often overlooked as a parameter to consider and optimize when choosing materials for excitonic devices, is emphasized

Effect of Molecular Stacking on Exciton Diffusion in Crystalline Organic Semiconductors

Exciton diffusion-is at the heart of most organic optoelectronic devices' operation, and it currently the most limiting factor to their achieving high efficiency. It is deeply related to molecular organization, as it depends on intermolecular distances and orbital overlap. However, there is no dear guideline for how to improve exciton diffusion with regard to molecular design and structure. Here, we use single-crystal charge-transfer interfaces to probe favorable exciton diffusion. Photoresponse measurements on interfaces between perylenediimides and rubrene show a higher photocurrent yield (+50%) am extended spectral coverage,(+100 nm) when there is increased dimensionality of the percolation network and stronger orbital overlap. This is achieved by very short interstack distances in different directional axes, which favors exciton diffusion by a Dexter mechanism. Even if the core of the molecule shows strong deviation from planarity, the similar electrical resistance of the different systems, planar and nonplanar, shows that electronic transport is not comproinised. These results highlight the impact of molecular organization in device performance and the necessity of optimizing it to take full advantage of the materials' properties